Regulator-based ink jet print cartridges are designed to handle air in the system that is left in the pen from manufacturing, air that enters during supply actuation, and air that is delivered to the pen from the ink supply. The air in the system is stored in the cartridge body and grows over time by diffusion; therefore, the cartridge has a limited lifetime before air causes failure. Storing air (also known as warehousing air) in the cartridge requires a large internal volume in which to accommodate air accumulation. These systems cannot be scaled down in size without compromising their useful life.
Methods of purging air from the cartridge body include purging air and ink through the nozzles, purging air and ink from another location besides the nozzles, and purging air only through an air permeable membrane that is impervious to ink. For all these methods except the membrane solution, a tank to store the wasted ink is required, which consumes a large volume in the printer, increasing its overall size. The membrane solution requires a very robust material that must last a lifetime of the pen, and because the material is very thin, these properties are difficult to achieve and therefore also make the material difficult to assemble into a cartridge.
Re-circulating ink delivery systems are inherently air tolerant. These types of systems move air and ink from the print head region of the pen, separate them in either a foam block or by gravity, and circulate the ink back to the print head. The driving force of the re-circulation is generally the same as that to deliver ink.
A fluid delivery system is disclosed. In an exemplary embodiment, the system includes a print cartridge and a fluid supply. The print cartridge includes a housing structure, an air-fluid separator structure within the housing structure, including an air vent region in communication with the separator structure. A fluid ejector is mounted to the housing structure, and a fluid plenum within the housing structure is in fluid communication with the fluid ejector. A fluid reservoir in the housing structure is in fluid communication with the plenum for supplying fluid to the plenum under negative pressure. A fluid re-circulation path is provided in the housing structure through the separator structure and the fluid plenum. A pump structure re-circulates fluid and air through the re-circulation path during a pump mode, wherein air bubbles may be separated from re-circulated fluid and vented to atmosphere from the air vent region. The fluid supply is continuously or intermittently fluidically coupled to the fluid reservoir.